Generally, movements which generate small abraded metal particles occur between the surfaces of contact in electrical contact units. These movements may have various causes. For example, in closed units very slow movements may occur because of thermal conditions, but also fast vibration movements may occur. Further, a sliding movement normally takes place between the surfaces of contact during the closing and breaking of conventionally designed contact units. Undependent of the cause and nature of the movements, the movements always will lead to wear of the contact units in the points of contact. This is a problem, and this particularily concerns such switches or corresponding devices where the surfaces of contact have been specially prepared in order to give good contact. Thus it is common practice to silver-plate the contact surfaces of the contact units in heavy power breakers. However, because of the relative movements between the connectors of the breaker, the silver-plating is damaged, and there is also a risk for spark formation because of the said generation of particles, so that the operation of the switch or breaker successively is impared, at the same time as the said generation of particles may give rise to disastrous sparkovers.